A water treatment for cleaning fluid by removing pollutants there from may use a heating method, a phase-changing method, or a separation membrane employing method.
The separation membrane employing method can realize high reliability since it is suitable for stably providing a desired water quality based on a size of pore formed in the separation membrane. Furthermore, it is unnecessary for the separation membrane employing method to perform a heating process. In this respect, the separation membrane employing method is advantageous in that it can be widely utilized in various separation processes using microbe that may be affected by the heating process.
The separation membrane may include a flat-type membrane having a flat cross section, and a hollow fiber membrane having a hollow therein. In case of the hollow fiber membrane, there are micro-pores provided on a surface of tubular fiber structure including inner and outer diameters therein, so that pollutants are filtered through the micro-pores included in the hollow fiber membrane. In comparison to the flat-type membrane, the hollow fiber membrane has the larger surface area owing to its inner and outer diameters. Accordingly, owing to the advantageous characteristics such as the large surface area of hollow fiber membrane, the hollow fiber membrane is widely utilized for the separation membrane in the recent applications of water treatment.
The hollow fiber membrane in type of a predetermined module is utilized in the water treatment, one type example of which is a submerged-type hollow fiber membrane module.
In order to form the submerged-type hollow fiber membrane module, the hollow fiber membrane module is submerged in a water tank filled with a fluid to be treated, and a negative pressure is applied to the inside of the hollow fiber membrane, whereby only fluid passes through minute pores of the hollow fiber membrane, thereby filtering out pollutants from the fluid by the minute pores included in the hollow fiber membrane.
The submerged-type hollow fiber membrane module is formed by steps of forming a bundle of hollow fiber membranes collected, and fixing the bundle of hollow fiber membranes in a module case, wherein theses steps are referred to as a potting process. When a sealing strength becomes weak between the module case and the bundle of hollow fiber membranes, the hollow fiber membrane module does not function properly due to the leakage of fluid. Accordingly, the potting process is a very important step in a method of manufacturing the submerged-type hollow fiber membrane module. In the related art, the potting process may be performed by a centrifugal molding method or immersion method.
In the centrifugal molding method, the plurality of hollow fiber membranes and the module case are put on a rotating body, a potting material is supplied to end portions of the hollow fiber membrane, and the rotating body rotates so as to fill the potting material in the plurality of hollow fiber membranes, thereby forming the bundle of hollow fiber membranes and fixing the bundle of hollow fiber membranes in the module case by the potting material.
This centrifugal molding method has the great sealing strength between the module case and the bundle of hollow fiber membranes since the potting material is filled in the hollow fiber membrane owing to the centrifugal force. However, the centrifugal molding method requires a cost for a centrifugal molding apparatus, for example, the rotating body and its driving apparatus. Whenever the module is changed in its size, it necessarily requires the replacement of parts in the centrifugal molding apparatus.
The immersion method performs the potting process without rotation. In case of the immersion method, after positioning the plurality of hollow fiber membranes in the module case, the potting material is supplied to the module case, whereby the potting material is charged in the hollow fiber membranes, thereby forming the bundle of hollow fiber membranes and fixing the bundle of hollow fiber membranes in the module case by the potting material.
The immersion method is advantageous in that it does not require a molding apparatus. However, the sealing strength between the module case and the bundle of hollow fiber membranes in the immersion method becomes lower than that in the centrifugal molding method.